# std::timed_mutex::try_lock_for

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< cpp‎ | thread‎ | timed mutex

template< class Rep, class Period > bool try_lock_for( const std::chrono::duration<Rep, Period>& timeout_duration ); |  | (since C++11)

Tries to lock the mutex. Blocks until the specified duration timeout_duration has elapsed (timeout) or the lock is acquired (owns the mutex), whichever comes first. On successful lock acquisition returns true, otherwise returns false.

If timeout_duration is less or equal timeout_duration.zero(), the function behaves like try_lock().

This function may block for longer than timeout_duration due to scheduling or resource contention delays.

The standard recommends that a std::steady_clock is used to measure the duration. If an implementation uses a std::system_clock instead, the wait time may also be sensitive to clock adjustments.

As with try_lock(), this function is allowed to fail spuriously and return false even if the mutex was not locked by any other thread at some point during timeout_duration.

Prior unlock() operation on the same mutex synchronizes-with (as defined in std::memory_order) this operation if it returns true.

If `try_lock_for` is called by a thread that already owns the mutex, the behavior is undefined.

### Parameters

timeout_duration | - | minimum duration to block for

### Return value

true if the lock was acquired successfully, otherwise false.

### Exceptions

Any exception thrown by timeout_duration (durations provided by the standard library never throw).

### Example

Run this code

    #include <chrono>
    #include <iostream>
    #include <mutex>
    #include <sstream>
    #include <thread>
    #include <vector>

    using namespace std::chrono_literals;

    std::mutex cout_mutex; // control access to std::cout
    std::timed_mutex mutex;

    void job(int id)
    {
        std::ostringstream stream;

        for (int i = 0; i < 3; ++i)
        {
            if (mutex.try_lock_for(100ms))
            {
                stream << "success ";
                std::this_thread::sleep_for(100ms);
                mutex.unlock();
            }
            else
                stream << "failed ";

            std::this_thread::sleep_for(100ms);
        }

        std::lock_guard<std::mutex> lock{cout_mutex};
        std::cout << '[' << id << "] " << stream.str() << '\n';
    }

    int main()
    {
        std::vector<std::thread> threads;
        for (int i{0}; i < 4; ++i)
            threads.emplace_back(job, i);

        for (auto& th : threads)
            th.join();
    }

Possible output:

    [0] failed failed failed
    [3] failed failed success
    [2] failed success failed
    [1] success failed success

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2093 | C++11 | `try_lock_for` threw nothing | throws timeout-related exceptions

### See also

lock | locks the mutex, blocks if the mutex is not available (public member function)
try_lock | tries to lock the mutex, returns if the mutex is not available (public member function)
try_lock_until | tries to lock the mutex, returns if the mutex has been unavailable until specified time point has been reached (public member function)
unlock | unlocks the mutex (public member function)

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